In a retrospective study of 100 patients with operable breast cancer, microscopic involvement of the nipple-areola complex was found in 16 cases. Each of these 16 cases occurred in patients with centrally situated tumours. In contrast, nipple involvement did not occur with peripherally situated tumours lying greater than 2 cm outside the areolar margin (P less than 10(-6), Fisher's exact test). Nipple involvement was more likely in patients with greater than or equal to 4 positive axillary nodes (P less than 0.01, chi 2 test). From this study it appears that nipple preservation may be undertaken during mastectomy for small peripheral tumours, provided the nipple is clinically normal, and frozen section analysis of the sub-nipple area is shown to be free from tumour invasion. These criteria for nipple preservation were satisfied in 20 patients out of a prospective series of 60. In this group, nipple preservation on the skin flap improved the cosmetic result of breast reconstruction in 35 per cent, and facilitated skin closure in 20 per cent. After a mean follow-up period of 50.4 months, nipple preservation was not associated with any significant excess of local recurrences.